Typically there are ducts carrying high temperature exhausts or other fluids extending into aircraft chambers which contain combustible materials. The ducts are insulated to prevent the heat of the fluid being carried from being transmitted into the chamber. In many instances it is necessary to terminate the insulation within such a chamber because of a change in the shape of the duct or because of a fitting which requires a different shape of insulation therearound. Where the insulation is terminated, it is necessary to retain it between the duct and the outer portion thereof which generally is covered with a very thin metal shell.
While these problems may occur with very low temperatures, the typical situation is with high temperatures. For example, in a typical duct in an aircraft the temperature of the fluid passing therethrough could be about 1000.degree. F. or 1100.degree. F. and the ambient temperature in the chamber could be about 225.degree. F. It also may vary down to minus 150.degree. F.
Where prior art metal flanges were secured to retain the end of the insulation and to support its cover outwardly of the duct, hot spots developed in the flanges, and where they extend over the insulation cover. For example, a solid metal flange raises the temperature along the flange at the exterior of the cover to about 550.degree. F. where the temperature in the duct is about 1025.degree. F. and the ambient temperature is 225.degree. F. This high temperature on the exterior of the insulation cover cannot be tolerated because of the combustible materials within the chamber. With the present invention under the same conditions, the temperature of the insulation cover at its end is raised only to 360.degree. F. with a 57% weight reduction in the flange.
In the prior art there are low conducting plastics, but they cannot stand the heat in the conditions under consideration. Similarly, ceramics could be used, but they are too heavy.